For aiding in understanding of the invention, a typical conventional splitting apparatus will be described with reference to FIGS. 9 and 10.
The apparatus comprises a pair of drive shaft 1, 2 extending parallel one above the other and driven by a motor (not shown) at the same speed in opposite directions as indicated by two arrows. Each of the drive shafts 1, 2 has fixed thereon a plurality of toothed wheels 5, 6, respectively, which are spaced at a predetermined interval along the axial direction of the drive shafts 1, 2, and each of which wheels 5, 6 has a number of teeth 3, 4 projecting radially outward. As shown in FIG. 10, each of the teeth 3, 4 has an incising edge 3a, 4a whose tip end extends straight and parallel to the axes of the drive shafts 1, 2. The toothed wheels 5, 6 are arranged on the drive shaft 1, 2 such that a plurality of pairs of upper and lower toothed wheels 5, 6 is provided wherein the wheels of each pair are radially aligned with each other with the incising edges 3a, 4a of the teeth 3, 4 on the wheels 5, 6 set in facing relation, as shown in FIG. 10, in the region of passage between the upper and lower toothed wheels 5, 6 through which a wood fiberboard is moved. The toothed wheels 5, 6 are secured to the drive shafts 1, 2 by means of keys 5a, 6a formed in the inner periphery of the wheels 5, 6 and engaged with grooves 1a, 2a in the outer periphery of the drive shafts 1, 2.
In the case of the splitting apparatus of FIGS. 9 to 11, each toothed wheel 5, 6 has a thickness of about 2 mm and an outer diameter of about 135 mm as measured with respect to a circle described by the tip ends of the teeth 3, 4. The two drive shafts 1, 2 are spaced vertically so as to provide a space of about 1 to 2 mm between the two circles which are described by the tip ends of the teeth 3, 4 of the toothed wheels 5, 6. Thus, the passage region is formed between the toothed wheels 5, 6, through which the wood fiberboard P is moved forward, or from left to right as seen in FIG. 9, by engagement with the teeth 3, 4 of the rotating wheels 5, 6.
Between each two laterally adjacent toothed wheels 5, 6 is provided a pair of pressure bars 7, 8 located one above the other. These pressure bars 7, 8 are fixed at the proximal ends thereof to a frame (not shown) of the splitting apparatus and have the opposite distal ends located beyond an imaginary vertical line E passing through the axes of the drive shafts 1, 2. As shown in detail in FIG. 11 which is an enlarged view of a circle F in FIG. 9, the end portions of the pressure bars 7, 8 are formed with flat surfaces 7a, 8a, respectively, each having a length of about 2 mm as measured along the fiberboard moving direction and making an angle of about 1.degree. with respect to a horizontal line passing perpendicularly to the imaginary line E so that the surfaces 7a, 8a provide slopes convergent as viewed in the moving direction of the fiberboard P and terminating at edges 7b, 8b. To be more specific, the slopes of the surfaces 7a, 8a are formed such that the edges 7b, 8b are spaced vertically at a distance corresponding to about 90% of the thickness of the fiberboard P to be split.
The apparatus further includes a splitting knife 9 fixed to the frame of the apparatus and extending in axial direction of the drive shafts 1, 2 with its cutting edge positioned adjacent the pressure bars 7, 8 and directed against the moving direction of the fiberboard P. The knife 9 has about 24.degree. of cutting angle and is disposed centrally with respect to the upper and lower toothed wheels 5, 6 so that the fiberboard P is split into two halves Pa, Pb or two separate layers of sheets having substantially the same thickness which is half the thickness of the material fiberboard P.
Between each two laterally adjacent toothed wheels 5, 6 on the downstream side thereof is provided a pair of separating bars 10, 11 located one above the other and having the proximal end thereof fixed to the frame of the splitting apparatus and the opposite distal end located adjacent to the knife 9. As shown in FIG. 9, the separating bars 10, 11 have surface 10a, 11a extending to intersect imaginary circles described by the tip ends of the teeth 3, 4 of the respective toothed wheels 5, 6 such that an obtuse angle is formed between these surface 10a, 11a and tangential lines of the above circles at the points of intersection, respectively.
A feeding conveyer 12, which is driven to travel at a speed corresponding to the peripheral speed of the toothed wheels 5, 6 at the tip ends of their teeth 3, 4, is disposed on the upstream side of the toothed wheel 5, 6 for feeding the fiberboard P, and two delivery conveyers 13, 14 are located on the downstream side adjacent to the separating bars 10, 11 for outfeeding split sheets Pa, Pb.
In operation of the above-described apparatus, the fiberboard P placed on the feeding conveyer 12 is moved toward the passage region between the toothed wheels 5, 6, where the fiberboard P is pierced or incised on both sides thereof by the teeth 3, 4 of the rotating wheels 5, 6, so that the fiberboard P is continued to move through the passage. As the fiberboard P is thus moved, its leading end is brought against the cutting edge of the stationary knife 9. As seen from FIG. 9, the cutting edge of the knife 9 is applied to the center of the fiberboard P as viewed across its thickness. As a result, the fiberboard P fed against the knife 9 is split by the knife 9 into to two separate sheets Pa, Pb with substantially the same thickness.
During the above splitting operation, the fiberboard P is pressed firmly from both top and bottom by the pressure bars 7, 8 at a position immediately preceding the cutting edge of the knife 9 for preventing a so-called presplit in the fiberboard P, thus making it possible to produce smooth split surfaces on the resulting sheets Pa, Pb. The split sheets Pa, Pb are pulled apart by the teeth 3, 4 of the rotating wheels 5, 6, moving past the tip end portion of the knife 9 along part of the periphery of the wheels 5, 6, until the sheets Pa, Pb are separated or removed successively from the teeth 3, 4 by the separating bars 10, 11 as shown in FIG. 9. The sheets Pa, Pb are guided onto the delivery conveyers 13, 14, respectively, and transferred to any subsequent process.
As an application of the resulting sheet Pa, Pb, it may glued, for example, to a plywood panel having a relatively rough surface in order to provide it with a smooth surface to which a decorative sheet such as sliced veneer sheet or vinyl chloride sheet is further laminated. The resulting product may be used as house interior materials such as flooring.
In the above-described conventional splitting apparatus, wherein the upper and lower toothed wheels 5, 6 or each pair are radially aligned and a number of teeth 3, 4 each having a straight edge 3a, 4a are provided circumferentially at a relatively short interval, the teeth 3, 4 on the toothed wheels 5, 6 tend to be brought into a harmful contact thereby to cause a breakage to the teeth 3, 4, for example, when the drive shafts 1, 2 on which the toothed wheels 5, 6 are mounted are caused to be bent by any force created during the splitting operation. Breakage of any teeth 3, 4 may cause a failure in transmission of force from the drive shafts 1, 2 to the fiberboard P via the toothed wheels 5, 6, so that splitting cannot be accomplished successfully. Accident of the above contact between the teeth 3, 4 may be forestalled by providing a space of at least about 1 mm between the two circles defined by the tip ends of the teeth 3, 4 of the wheels 5, 6.
For example, in handling a fiberboard with a relatively small thickness of about 1.5 mm with the above spacing set at about 1 mm, the teeth 3, 4 cannot incise sufficiently deep into the fiberboard for steady feeding and, therefore, successful splitting cannot be accomplished. When splitting a relatively hard fiberboard, the teeth 3, 4 cannot incise sufficiently deep into the fiberboard, either.
The above problems may be solved by arranging such that the toothed wheels 5, 6 are set off from each other in the axial direction of the drive shaft 1, 2 or disposed in a staggered manner so that the teeth 3, 4 on the wheels 5, 6 do not face each other in the board passage region and hence have little chance of tooth-to-tooth contact. In such an arrangement of the toothed wheels 5, 6, however, the top and bottom pressure bars 7, 8 of each pair must be disposed accordingly in an offset relation to each other. In such a disposition of the pressure bars 7, 8, the fiberboard P cannot be pressed firmly enough to produce smooth split surfaces on the resulting sheets Pa, Pb.